1. Field of the Invention
This invention relates generally to laser assemblies, and more particularly to a widely tunable laser assembly with an integrated modulator.
2. Brief Description of the Related Art
A laser transmitter for fiber optic networks must provide signals at a given stable wavelength, modulated at a desired rate with low chirp and an appropriate power launched into optical fiber. Current networks have as many as 100 wavelength channels with one laser devoted to each channel, and each laser having an external modulator. Significantly greater efficiencies could be realized with a laser transmitter and a modulator included on a chip, wherein the modulated laser is capable of being tuned to cover every channel of a system.
Photonic integration can be used to provide a laser transmitter on a chip, as is well understood in the art. FIG. 1 shows a block diagram of a structure that can be used to accomplish this. While photonic integration is well known in the art, prior art efforts have been focused on the integration of lasers that are not widely tunable. Kobayashi, N.; Noda, A.; Watanabe, T.; Miura, S.; Odagawa, T.; Ogita, S. xe2x80x9c2.5-Gb/s-1200-km transmission of electroabsorption modulator integrated DFB laser with quarter-wavelength-shifted corrugation,xe2x80x9d IEEE Photonics Technology Letters, vol. 11, (no.8), IEEE, August. 1999. p.1039-41;Delprat, D.; Ramdane, A.; Silvestre, L.; Ougazzaden, A.; Delorme, F.; Slempkes, S. xe2x80x9c20-Gb/s integrated DBR laser-EA modulator by selective area growth for 1.55- mu m WDM applications,xe2x80x9d IEEE Photonics Technology Letters, vol.9, no.7, IEEE, July 1997. p.898-900. Large tuning ranges make achieving adequate performance of these functional blocks non-obvious with respect to the teachings of the prior art in general, and the prior art related to narrowly tunable devices in particular. What is needed is photonic integration techniques to construct a widely tunable laser apparatus including an integrated modulator.
Accordingly, an object of the present invention is to provide a laser assembly where all of the elements are fabricated on a single wafer.
Another object of the present invention is to provide a diode laser assembly with the elements derived from a common epitaxial layer structure.
A further object of the present invention is to provide a widely tunable diode laser assembly with an integrated modulator.
Yet another object of the present invention is to provide a diode laser assembly with the elements fabricated on a single wafer by common process steps.
A further object of the present invention is to provide a monolithically integrated diode laser assembly using fabrication steps that tailor optical properties of selected regions to a desired electro-optic function.
Another object of the present invention is to provide a monolithically integrated diode laser assembly that uses common fabrication process steps to form the apparatus elements that are compatible with photonic device fabrication processes presently used in the lightwave industry.
These and other objects of the present invention are achieved in a laser assembly that includes an epitaxial structure formed on a substrate. A laser resonator, a modulator and a coupler are formed in the epitaxial structure. The coupler is positioned to receive and adjust an output received from the modulator.
In another embodiment of the present invention, a laser assembly includes a first semiconductor layer and a second semiconductor layer in an epitaxial structure. The first and second semiconductor layers have different dopings. A waveguide layer is formed between the first and second semiconductor layers. The first waveguide layer includes a first reflector and a second reflector. An optically active gain medium is disposed between the first and second reflectors. The first and second reflectors define a laser resonator. A modulator is formed in the epitaxial structure outside of the laser resonator. A coupler is formed in the epitaxial structure. The coupler is positioned to receive and adjust an output received from the modulator.